Retention of Maxillofacial Prosthetics

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Transcript of Retention of Maxillofacial Prosthetics

By : Yasser Araby BDS, MSc, DDSc ( Prostho.)Maxillofacial DeformitiesIII. Mechanical RetentionTraditional TeachingTraditional TeachingFocuses on teaching, not learning. Teacher centered approach.Passive Learning.Not every ounce of teaching = 1 ounce of learning.Retention of Maxillofacial AppliancesIt can be classified into; Congenital defects.Acquired defects.Developmental defects.Congenital cleftAcquired defects caused by gun shotDisfigurment following Surgery for malignant lesionCocaine induced palatal defectSurgicalCombinationModaliteis of ManagementProstheticMaxillofacial Prosthetics is " The branch of Prosthodontics concerned with the restoration and/or replacement of the stomatognathic and craniofacial structures with prostheses that may or may not be removed on a regular or elective basis"Types of Maxillofacial Restorations1. Intra-oral Restorations : ex. Obturators , prosthesis for congenital defects, stents, splints, resection appliance 2. Extra-oral Restorations : ex. Orbital, occular, Auricular, Nasal, Midfacial prostheses, Cranial implants, Radium sheild.3.Combined Intra-oral and Extra-oral Restorations.RetentionSupportPrimary factors for the success of the ProsthesisStabilityTypes of Retention in Maxillofacial AppliancesAnatomical RetentionAdhesive RetentionMechanical RetentionOsseointegrated ImplantsI. Anatomical RetentionIntraoral Anatomical RetentionMaxillary ConsiderationsMandibular ConsiderationsExtraoral Anatomical RetentionOrbital DefectsNasal DefectsAuricular DefectsSurgical Modifications enhancing Maxillary Prosthesis retention and prognosisPreservation of maxilla.Coronoid process removal, When?Retention of Key teeth. How?Skin graft linning. Why ?Mucosal coverage for bony margin. Removal of remaining part of soft palate, When?Creation of undercut, Where?Surgical Modifications enhancing Mandibular Prosthesis retention and prognosisTeeth preservation.Median incision, How?Suturing of lingual frenum.Lingual sulcus preservation, Where?Digastric Ms & Hyoid Ms, What?Half circle cut across the ramus.Anatomical Retention of the ObturatorResidual Maxillary RetentionWithin the defect retentionTeeth.Alveolar ridge.Residual soft palateResidual hard palateAnterior nasal spineLateral scar bandHeight of the lateral wallSurgical guidelines enhancing extra oral prosthetic rehabilitationRemoval of unsupported soft tissues.Round sharp bony edges.Negative space ( concavity )is required.Use split thickness flap.Limit the bulk of the flap.Special considerations for each type of defect.II. Adhesive RetentionMaxillofacial Prosthetic Adhesive:a material used to adhere external maxillofacial prostheses to skin and associated structures around the periphery of an external anatomic defect.Acrylic Resin AdhesiveSilicone Adhesives(cc) photo by medhead on FlickrAdvantagesDisadvantagesVs(cc) image by anemoneprojectors on FlickrReadily available.Easily appliedEasily manipulated.Satisfactory retention for limited periods of time.No surgical procedures.Less expensive as compared to implants.Irritation and allergy.Affected by skin movement.Affected by humidity.Effective only in hair free bed.Damage of the margin.unsuitable with poor dexterity.Poor hygiene.Debonding / peel phenomena.(cc) image by nuonsolarteam on FlickrEyeglassesEyeglasses:Effective with nasal and orbital defects.Advantsges: easily adjusted, light weight, hidden margins.Disadvantages: All time wear, poor fit margin, unsuitable in cases with lost supraorbital ridges.Opaque lenses. Why?Acrylic frame. Why?Additional mean of retention.Bone Screw Retention13 - 16 mm self tapping titanium or stainless steel screw placed in the palatal vomer through a midpalate hole predrilled through the acrylic resin baseplate ( surgical obturator) in the mid palateSuture Retention2-0 silk sutures can passed through six to eight predrilled holes in the acrylic resin baseplate . Each suture is secured with a knot against the denture flange in the middle of the suture and each one passed through soft tissue and tied.Circumzygomatic wire retentionWires are passed over the zygomatic arch and threaded through two bilateral holes placed in the premolar area of the baseplate flange. It is used for retention of the surgical obturator as well as for the retention of the gunning splints.Retentive tapes and elastic loopsIt is widely used in nasoalveolar molding for the cases of congenital cleft lip and palate.There are many variations to this described form of retentive tapes and elastic bands , others can used extraoral wire extension that attached to head bands.Clasps

The degree of Retention obtained by the clasp is varible according to :

1. Length of the retentive clasp arm. 2. Diameter of the retentive clasp arm. 3. Form of the retentive clasp arm. 4. Material of Retentive clasp arm. 5. Contour of retentive clasp arm. 6. Depth of the undercut employed.General considerations for obturator frameworkRetentive elements >> far & close to defect.Additional clasps >> indirect retention.Maximumsupport >> restsMaximum resistance >> guiding planes.Rigid major connectors.Lingual retention arms. > > most posteriorDesign PossibilitiesAramany class I tripodal obturator design for curved arches.Aramany class I linear obturator design is used for class I defect when there are no anterior teeth present or when one doesnot desire to use anterior teeth and remaining posterior teeth are in a relatively straight line.Aramany class II obturator designAramany class III obturator design.Aramany class IV obturator is a linear design because of presence of only posterior teeth in a straight line. Retention is problematic. Combination of buccal and lingual retention may be necessary if useful retention cannot be found within defect.Aramany class V obturator designAramany class VI obturator designSwing Lock DeviceThe mechanical retention provided by S/L design is an excellent mean of cantilever suspension. The requirement for S/L is the presence of 6 - 8 mm vestibular depth and at least 4 teeth span for labial bar.Retention is supplied by small vertical struts that leave the labial or buccal bar, traverse the marginal gingiva (with relief to avoid impingement), and contact the gingival third of the abutment teeth. The desired amount of undercut is 0.25 mm.(0.01inch). these stuts are passive at rest.The most critical aspect of the S/L design is the arc of closure (AOC).TelescopingIt is often used when an overlay denture is planned or an extremly malposed tooth is needed for stability, It is also used when a major change in the vertical or centric dimension is indicated as in cleft lip and palate , prognathic mandibles or resected mandibles.Telescope crowns reduce the destructive horizontal and rotational occlusal forces by directing them more axially and less traumatically than other retainers.AttachmentsAdvantages:Easthetic enhancement & functional rigidity especially ( class II & III ) defects.Superior retention & stability.Bar type >>> splinting.decrease effects on dental health by decrease size.Attachments in maxillofacial prosthetics:Improve retention obtained from incisors.Should be resilient to accomodate obturator movement.Retentive elements applied only upon dislodgment.Rest seat should be prepared on the adjacent abutment to direct forces & reduce attachment wear.For combining intraoral & extraoral prostheses ( pins and tubes / bolts)Magnetic RetentionAdvantges:Dissipate lateral forces.less need for parllel abutments.simple technique.Disadvantages:Corrosion problem.Short life span of intraoral magnets.Uses:Overdentures, obturators, facial prothesis and implants.Sectional Prosthesis to acheive appropriate path of insertion.Combination of intraoral and extraoral prostheses.ZygomaticIntaoralImplant RetentionExtraoralCraniofacial ImplantsIt differs from conventional implants in size and design.Advantages:1. Enhanced and reliable retention.2. Retention is not affected by environmental factors.3. Facilitated proper positioning of th prosthesis.4. Improved convenience of wearing the prosthesis.5. Preservation of the edges of silicone prostheses.Implants & Auricular Defects:Provide excellent cosmetic results. Iplants placed in the temporal bone ( posterior superior quadrant.Adequate hygiene is a problem.Highest success rate followed by nasal then orbital.(cc) image by nuonsolarteam on FlickrNasal Defects:The primary site of choice for implant placement is the anterior nasal floor.

Because implant retention is possible at the inferior aspect of the prosthesis only, it is critical that the design of the retentive elements of the prosthesis incorporate two planes of retention. Generally a “U” shaped retentive bar, connected to the implants at the base of the “U,” will provide three points for retention, the two vertical struts and the horizontal crossbar.Orbital Defects:Small orbital defects may not be suitable for implant supported restorations The implants are generally located in the supraorbital rim or in the lateral rim of the residual orbit. Medial placement of the implants is discouraged due to diminished bone quantity and quality in this area and the associated lowered implant survival rates in bone of low quality.Mandibular Defects:The reconstructed mandible will be edentulous in the graft site. Endosseous implants in this grafted bone will (Internal loading ) of the graft results in bone preservation.The resected mandible which has not been reconstructed will have a deviated opening and closing arc >> Forces on the implant.Clinical experience with fixed implant supported mandibular resection prostheses has shown promising results despite the concerns over the angular force application.Maxillary Defects:When implants are used to retain such prostheses it is essential that the different forces be considered. These prostheses will have a tendency to rotate into the defect area when occlusal loads are placed on the defect side and they will have the tendency to rotate out of the defect area as gravity exerts its pull on the prosthesis. Endosseous implants in residual maxilla must be of sufficient number, length and distribution to resist the anticipated complex forces from mastication and dislodgment.Zygomatic ImplantsRecent TrendsCAD & Rapid Prototyping3D Laser Scanning: is a non-contact, non-destructive technology that digitally captures the shape of physical objects (e.g patientˋs face) using a line of laser light. 3D laser scanners create “point clouds” of data from the surface of an object. In other words, 3D laser scanning is a way to capture a physical object’s exact size and shape into the computer world as a digital 3-dimensional representation.Computer-Aided Design (CAD), is the use of computer software and systems to design and create 2D and 3D virtual models of goods and products for the purposes of testing.

Rapid prototyping : is the automatic construction of physical objects using solid freeform fabrication. Rapid prototyping takes virtual designs from Computer Aided Design (CAD) or animation modeling software, transforms them into thin, virtual, horizontal cross-sections and then creates each cross section in physical space, one after the next until the model is finished.3D Laser scanningCAD model for face and prosthesis